In recent years, ink-jet recording systems, which enable simple formation of images at low cost, have been applied to various printing fields such as photography, various printing, and special printing such as marking and color filters. Specifically, by employing ink-jet recording apparatuses which eject minute controlled dots of ink, ink-jet inks which have been improved in color reproduction, durability, and ejection adaptability, and specialized paper media which have been enhanced in color forming properties of colorants and surface glossiness, it has become possible to achieve image quality comparable to conventional silver halide photography. Image quality of the present ink-jet recording systems is enhanced only when an ink-jet recording apparatus, an ink-jet ink and a specialized paper medium are simultaneously improved.
However, ink-jet systems which require specialized kinds of paper result in problems such that recording media are limited and use of such recording media increases cost. Accordingly, many trials have been conducted in which recording, employing the ink-jet systems, is carried out on transfer media which differ from specialized kinds of paper. Specific systems include a phase-changing ink-jet system employing a wax ink which is solid at room temperature, a solvent based ink-jet system employing rapidly drying organic solvents as a main component, and an actinic radiation curable ink-jet system in which, after recording, actinic radiation such as ultraviolet radiation (UV radiation) is exposed onto the deposited ink to result in crosslinking.
Of these, the UV radiation curable ink-jet system results in relatively low unpleasant odor, compared to a solvent based ink-jet system, whereby an example of the ultraviolet radiation curable ink-jet inks is disclosed (refer to Patent Document 1).
However, even though these actinic radiation curable ink-jet inks are employed, dot diameter after deposition of ink droplets varies markedly, whereby it has been impossible to form highly detailed images on various recording media.
In recent years, a number of ultraviolet radiation curable ink-jet inks, employing cationically polymerizable monomers, have been proposed. Such ultraviolet radiation curable ink-jet inks are not subjected to inhibition due to oxygen, but result in a problem in which they tend to be adversely affected by molecular level moisture (namely ambient humidity). Further, depending on ambience during curing, a problem occurs in which wrinkling is generated due to contraction during curing.
Image formation via the ultraviolet radiation curable ink-jet system is characterized in that it is possible to produce high quality images at low cost and to form images onto recording media which absorb no ink. However, inherent problems of the above ultraviolet radiation curable ink-jet system exist. For example, in cases in which images are formed on recording media which absorb no ink, when curing capability of ink is insufficient, image quality is markedly degraded due to mixing of a deposited dot with adjacent dots. Specifically, when formation of highly detailed images is demanded, mixing of colors of deposited dots results in critical problems. To overcome the above drawbacks, disclosed are actinic radiation curable ink-jet inks which employ, as a photopolymerizable compound, oxirane compounds, vinyl ether compounds, and oxetane compounds (refer to Patent Documents 2 and 3). Further disclosed are actinic radiation curable ink-jet inks which employ, as a photopolymerizable compound, alicyclic epoxy compounds and oxetane compounds (refer to Patent Documents 4 and 5). However, in each of the above proposed methods, desired curability and ejection capability, and formation of high quality images without generation of wrinkling are not simultaneously realized.
Further, application of the ultraviolet radiation curable ink-jet inks to outdoor advertisements is expected since they are highly water resistant. For application to outdoor advertisements, visibility is important, and inks, which result in high chroma, are demanded to reproduce bright colors. When conventional inks are employed, in order to enhance chroma, it has been required to increase the amount of deposited ink or the amount of pigments in the ink. However problems occurred in which an increase in the deposited amount resulted in an increase in the feel of unevenness and non-uniformity of glossiness, while an increase in concentration of pigments resulted in unstable discharge due to poor discharge capability.
Among high-class pigments, known are metal complex pigments which exhibit high durability such as high lightfastness or high heat resistance, and high color forming capability. Specifically, with regard to metal complex pigments of azo compounds, examples of radically photopolymerizable systems for color filters are disclosed (refer to Patent Documents 6-8).
However, heretofore no examples have been found in which ink prepared by dispersing the metal complex pigments of azo compounds into cationically polymerizable monomers is applied to an actinic radiation curable ink-jet ink. In addition, no examples have been found in which desired storage stability, ejection stability and curability are realized, and when cured after ink ejection, highly detailed image quality is realized which exhibits high density, results in uniform glossiness and no wrinkling.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 6-200204 (claims and examples)
(Patent Document 2) JP-A No. 2001-220526 (claims and examples)
(Patent Document 3) JP-A No. 2002-188025 (claims and examples)
(Patent Document 4) JP-A No. 2002-317139 (claims and examples)
(Patent Document 5) JP-A No. 2003-55449 (claims and examples)
(Patent Document 6) JP-A No. 2001-152039 (claims and examples)
(Patent Document 7) JP-A No. 2001-354869 (claims and examples)
(Patent Document 8) JP-A No. 11-14825 (claims and examples)